1. Field of the Invention
The present invention relates to a sealing tape for an ink jet recording head detachably adhered to protect the surface of a chip which is provided on an ink jet recording head and on which discharge ports for discharging ink are formed, and also relates to an ink jet recording head using such a sealing tape.
2. Description of the Related Art
The discharge ports of an ink jet recording head are open to the atmosphere since ink is discharged therefrom during usage. On the other hand, during the non-usage times, the surface of the ink jet recording head on which the discharge ports are arranged is capped so as to prevent clogging of the discharge ports resulting from evaporation of ink solvent through the discharge ports and contact-related damage.
The discharge ports can be protected by capping when the ink jet recording head is mounted on an apparatus such as a printer. However, when the ink jet recording head is not mounted on an apparatus, in particular, when it is being transported, it is necessary to prevent evaporation of ink solvent and contact-related damage by other means. For this reason, the chip surface including the ink discharge ports is generally protected by a sealing tape having adhesive properties as described in U.S. Pat. Nos. 5,262,802, 5,781,208, 5,850,238, or Japanese Patent Application Laid-Open No. H03-248849.
Japanese Patent Application Laid-Open No. 2007-326965 describes that an acrylic adhesive, a silicon-based adhesive, a rubber-based adhesive (e.g., adhesives containing natural rubber, synthetic rubber, reclaimed rubber, thermosetting rubber, styrene-isoprene-styrene), and a petrolatum-based adhesive can be used as the adhesive layer of the sealing tape.
However, if the sealing tape adhered to the ink jet recording head has too strong an adhesive strength, the ink jet recording head may be damaged when the sealing tape is detached. For this reason, U.S. Patent Application Publication No. 2007/263034 describes a technique for changing the adhesive strength of the sealing tape depending on the position on the discharge port surface.
In recent years, demands for higher resolution image recording have increased, and it is necessary to decrease the amount of ink discharged from the discharge ports of the ink jet recording head to increase resolution.
In a typical ink jet recording head, a resin film is formed on a substrate on which discharge energy generating elements such as heaters or piezoelectric elements are formed, and ink channels are formed in the resin so as to correspond to a predetermined number of discharge energy generating elements. Then, discharge ports are formed by communicating the respective channels to the resin surface. Such an ink jet recording head has a hollow structure in which channels and the discharge energy generating elements such as heaters are formed inside the peripheries of the discharge ports.
In the ink jet recording head having the described structure, the distances between the discharge energy generating elements such as heaters and the discharge ports affect the ink discharge amount, and the distances can be determined by the thickness of the resin film. For this reason, in order to decrease the amount of ink discharged from the discharge ports to increase resolution, it is necessary to decrease the thickness of the resin film that forms the discharge ports. Furthermore, when the discharge ports are formed to be closer to each other, the hollow structure at the peripheries of the discharge ports tends to have a higher hollow ratio. As a result, the resin film that forms the discharge ports may become weak against external stress. Therefore, it is necessary to adjust the adhesive strength of the sealing tape for the ink jet recording head adhered to the resin film to the extent that it will not damage the resin film when detached. For example, an extremely high adhesive strength may cause damage to the ink jet recording head when the sealing tape is detached.
In general, adhesives fluidize with time right after being adhered to an adherend and spread out to infiltrate the adherend, thus increasing the contact area and increasing its adhesive strength. Similarly, the adhesive strength of the sealing tape using an adhesive increases with time during storage for transportation right after being adhered to the chip surface.
As described above, the sealing tape for the ink jet recording head aims to prevent clogging of the discharge ports resulting from evaporation of the ink solvent through the discharge ports and contact-related damage. For this reason, during periods immediately after adhering and before usage, it is necessary to maintain a constant, sufficient adhesive strength so that the sealing tape is not detached due to a lack of adhesive strength. On the other hand, the adhesive strength should be adjusted to the extent that it will not damage the ink jet recording head when detached.
If the sealing tape is designed to have a sufficient adhesive strength right after adhering, since the adhesive strength increases after temporal change, there is a concern of damage to the ink jet recording head at the time of detachment. On the contrary, if the adhesive strength increased after temporal change is adjusted to the extent that it will not damage the ink jet recording head, there is a concern of a lack in the adhesive strength right after adhering. Since the hollow ratio of the hollow structure at the peripheries of the discharge ports increases with the increased demand for higher resolution image recording, it is expected that this tendency will become more conspicuous.
As described in U.S. Patent Publication No. 2007/263034, a technique has been used hitherto as a countermeasure in which the adhesive strength of the sealing tape is changed depending on the position of the discharge port surface. However, this countermeasure will result in increased number of production steps, thus complicating the process, and requires more expensive facilities. Thus, further improvement is desirable.
Although various adhesives have been studied to solve these problems, in the case of sealing tapes for the ink jet recording head, it is necessary to suppress deterioration of the adhesive resulting from reactions (attack) with ink components being used, in addition to adjustment of the adhesive strength described above. Moreover, there are various limitations in maintaining the characteristics of ink being used; for example, it is necessary to reduce the components eluted from the adhesive. Therefore, regarding adhesives used in the ink jet recording head, a unique adhesive composition is essential.